This invention relates to aliphatic polyester resin compositions, molded articles of aliphatic polyester resin and methods of their production.
From the point of view of protection of natural environment, biodegradable resins and molded articles produced from them are recently coming to be considered desirable, and aliphatic polyester resins such as polylactic acid resins and their molded articles are coming to be particularly noted. Although many of aliphatic polyester resins are essentially crystalline resins, they are slow to crystallize and behave nearly like a non-crystalline resin at the time of molding such that molded articles produced from them have many problems. In view of these problems, therefore, aliphatic polyester resins are usually presented in the form of aliphatic polyester resin compositions with a nucleating agent for crystallization or also some other additives, if necessary, when used for molding. This invention relates to improvements in the production method of such aliphatic polyester resin compositions.
Known prior art examples of nucleating agent to be contained in aliphatic polyester resin for producing an aliphatic polyester resin composition include: (1) compositions with melting point at 40-300° C. selected from amides of aliphatic carboxylic acid, amides of aliphatic bis-carboxylic acid, N-substituted bis-amides of aliphatic carboxylic acid and N-substituted ureas (as disclosed, for example, in Japanese Patent Publication JP1997-278991); (2) aromatic amide compounds such as trimesic acid-tris-(t-butyl amide), 1,4-cyclohexane dicarboxylic acid dianilide, 2,6-nephthalene dicarboxylic acid dichlorohexyl amide, N,N′-dibenzoyl-1,4-diamino cyclohexane and N,N′-dicyclohexane carbonyl-1,5-diaminonaphthalene (as disclosed, for example, in Japanese Patent Publication JP1998-87975); (3) organic compounds with melting point or softening point 80-300° C. and having specified melt-entropy (as disclosed, for example, in Japanese Patent Publication JP1999-5849); (4) metal salts of organic phosphate ester and basic inorganic aluminum compounds (as disclosed, for example, in Japanese Patent Publication JP2003-192883); (5) p-toluene sulfonic acid and its metallic salts (as disclosed, for example, in Japanese Patent Publications JP1996-120165 and JP1999-240962); (6) sodium sulfoisophthalate (as disclosed, for example, in Japanese Patent Publication JP2003-240962); and (7) inorganic particles such as talc (as disclosed, for example, in Japanese Patent Publication JP1996-3432). These prior art aliphatic polyester resin compositions, however, still have the same problems in that they are slow in crystallization and hence it takes a long time at a relatively high temperature for the molding process. Moreover, the molded products made from them are likely to undergo deformation at the time of mold releasing, and the physical characteristics of these molded products are inferior.